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II E> R.ARY 

OF THE 
UNIVERSITY 
Of ILLINOIS 

590.5 

FI 
v. 37-38 



BIOLOGi 



^,est Date stamped below 




L161 O-1096 



Parallelism in the Evolution of the Permian 
Reptilian Faunas of the Old and New Worlds 

Everett C. Olson 1 
Research Associate, Division of Paleontology 

INTRODUCTION 

When vertebrate remains were first encountered in the San 
Angelo Formation of Texas, we could not avoid speculations about 
resemblances of the newly found reptiles to mid-Permian forms of 
Russia and South Africa. Doubtless part of the speculation was 
prompted by a subconscious feeling that the fossils from these 
areas should show resemblances. It soon became apparent, however, 
that in size, at least, some of the North American reptiles did 
rival the largest of the relatively gigantic forms of the Old World 
mid-Permian. A more thorough study has shown that there is a 
notable similarity of adaptive types and that evolution, which 
appears to have been independent in the Old and New Worlds 
during the Permian, has produced a number of interesting paral- 
lels. Furthermore, it would appear that there is a rough time 
equivalence of the rocks in which these adaptive counterparts 
appear in the Old and New Worlds. 

By the time that deposition of the San Angelo beds of north 
central Texas was taking place, the old, familiar, earlier Permian 
deltaic fauna had disappeared, at least in the Texas area, and had 
been replaced by a strikingly different assemblage. At about the 
same time, in Russia and South Africa, there appeared assemblages 
unknown from any earlier deposits. The Old World faunas have 
been studied for many years and described and discussed in nu- 
merous publications. The San Angelo forms have been known but 
a short time. Their general structure and relationships to earlier 
reptiles were considered in some detail in an earlier paper (Olson 

1 Professor of Vertebrate Paleontology, University of Chicago 

385 



386 FIELDIANA: ZOOLOGY, VOLUME 37 

and Beerbower, 1953). Field work in 1953 and 1954 has added 
greatly to the knowledge of the described genera but has increased 
the generic list of seven only by one or two possible additions. In 
1953 a find was made in the Flower Pot Formation, which directly 
overlies the San Angelo Formation in Texas (Olson, 1954). The 
specimens from this formation, with one or two exceptions, appear 
to be congeneric with members of the San Angelo assemblage. Field 
work has now been sufficiently extensive that it appears unlikely 
that the list of genera will be materially increased by additional 
work in the Texas area. It is thus a rather small array of genera 
that provides a basis for comparisons with the more extensive as- 
semblages of Russia and South Africa. Even so, the comparisons 
yield much that is of interest in the areas of evolution and zoo- 
geography. It is the principal purpose of this paper to outline the 
evolutionary history that led to the development of these assem- 
blages, to compare the assemblages, and to attempt to evaluate 
their meanings. 

There are, of course, many problems in such a study, and the con- 
clusions must be considered in light of the difficulties. There is 
the problem of correct evaluation of the role of each species in the 
economy of the ecological system, the problem posed by the lack of 
information about the totality of the systems, the problem of corre- 
lation between continents, and that posed by the incomplete nature 
of the record of ancestral stocks. An effort has been made through- 
out this paper to point out the specific nature of these difficulties 
and the ways in which they have affected interpretations. 

THE GROUPS OF ANIMALS CONSIDERED 

Since the San Angelo and Flower Pot assemblages are almost 
exclusively reptilian, comparative studies are restricted to this class 
of animals. The major groups and pertinent subgroups that play 
an important part in the study are given in the classification on 
page 387. 

The Diadectomorpha and Captorhinomorpha are often grouped 
into a single order of primitive reptiles, order Cotylosauria, in spite 
of the fact that the association has been repeatedly questioned by 
prominent students in the field. In the present analysis, the two 
groups play very different roles, and for this reason, if no other, they 
must be considered separately. Early captorhinomorphs were small 
and were lizard-like in general proportions. They appear to have 
been fast-running, carnivorous to omnivorous, terrestrial animals 



OLSON: EVOLUTION OF PERMIAN REPTILIAN FAUNA 387 

Class Reptilia 

Subclass Parareptilia 1 
Infraclass Diadecta 

Order Diadectomorpha 
Family Diadectidae 
Family Pareiasauridae 
Family Procolophonidae 
Subclass Eureptilia 

Infraclass Captorhina 

Order Captorhinomorpha 
Suborder Captorhinomorpha 
Infraclass Synapsida 
Order Pelycosauria 

Suborder Ophiacodonta 
Suborder Sphenacodontia 
Suborder Edaphosauria 
Family Edaphosauridae 
Family Caseidae 
Order Therapsida 

Suborder Titanosuchia 
Suborder Tapinocephalia 
Suborder Anomodontia 
Suborder Theriodonta 
Infraorder Gorgonopsia 
Infraorder Therocephalia 



and to have played an important role in the early faunas. Later in 
their history, large herbivores, up to five or six feet in length, 
developed. Diadectes and other closely related genera represent the 
Diadectomorpha in the late Pennsylvanian and early Permian. 
They were heavy-bodied, slow-moving herbivores. They were suc- 
ceeded later in the Permian by the massive, herbivorous pareia- 
saurs, and the lightly built, small procolophonids. The latter appear 
to have been adaptively similar to some of the smaller and earlier 
herbivorous captorhinomorphs. 

Pelycosaurs were primitive mammal-like reptiles. The earliest, 
the ophiacodonts, appear to have arisen directly from primitive 
captorhinomorphs and to have accentuated the carnivorous poten- 
tialities of the ancestral stock. From the ophiacodonts came the 
active, highly predaceous sphenacodonts, of which Dimetrodon is 
the best known representative. The source of the edaphosaurians 
is less certain. The genus Edaphosauria, genotype of the family 
Edaphosauridae, occurs very early, near the beginning of the pely- 
cosaur record. The caseids appeared first in the early Permian and 

1 Classification after Olson (1947). 



388 FIELDIANA: ZOOLOGY, VOLUME 37 

became prominent only in the upper beds of this time. Both 
families consisted in large part of rather ponderous, slow-moving, 
terrestrial to semi-aquatic herbivores. 

The therapsids, which were advanced mammal-like reptiles, 
probably arose from the sphenacodonts. There seems to be no doubt 
that this was the origin of the titanosuchids and theriodonts. The 
source of the tapinocephalids and anomodonts is less certain, but a 
sphenacodont ancestry seems most probable. If this was the case, 
later sphenacodont history set the stage for radiation into herbiv- 
orous modes of life as well as for increased adaptive spread in the 
carnivorous realm. This concept is important in the interpretation 
of the early radiation of therapsids and in evaluation of the dif- 
ferences between Old and New World radiations in the mid-Permian. 

The fact that only reptiles can be considered in our comparisons 
limits the interpretation of faunal evolution. Undoubtedly both 
fish and amphibians, among the vertebrates, invertebrates, and 
plants, played a role in the modifications of the reptiles. Xenacanth 
sharks, primitive actinopterygians, dipnoi, and crossopterygians, 
among the fish, and lepospondylous and apsidospondylous amphib- 
ians are components of the Permian vertebrate faunas. The roles, 
both minor and major, that they have played in a Permian chrono- 
fauna have been discussed for the Clear Fork of North America 
elsewhere (Olson, 1951). It may be assumed that they were equally 
effective in less well-studied faunas and that their impact was in 
large part a function of the adaptive types present in a given area. 
Fortunately for our purposes, the taxonomic groups were widely 
dispersed in the Pennsylvanian and early Permian, and similar adap- 
tive types within the higher categories occur in the various areas 
that have been studied. Thus, the fish and the amphibians 
probably played rather similar roles in the economy of contemporary 
ecological structures in the areas with which we are concerned. 
There seems fair justification for an assumption that, in a broad 
sense, the effects of fish and amphibians were more or less constant 
in the various areas during the time considered and that differences 
in reptilian evolution were dependent largely on other factors. 
Knowledge of directly associated invertebrates during this time is 
very slight. Understanding of the plants is somewhat better, but no 
co-ordinated studies to evaluate the effects of botanical differences 
have been made. It is beyond the scope of this report to attempt 
an evaluation of the effects of differences in the plants, but it seems 
probable that they were of considerable importance. 



OLSON: EVOLUTION OF PERMIAN REPTILIAN FAUNA 389 
GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION OF REPTILES 

The pertinent data are summarized in Table 1. There are, 
however, certain problems of contemporaneity of faunas that need 
to be considered, and important points of spatial and temporal 
distribution that require special emphasis. These can be treated by 
a systematic summary of the temporal sequences: 

1. Late Pennsylvanian (Stephanian) : The striking resemblances 
between the North American and European middle to late Stephanian 
vertebrate faunas have been discussed in some detail by Romer 
(1945) in his comparison of the North American faunas with that 
from Kounova in Bohemia. The general aspects of these faunas 
show clearly that they can be considered ancestral to the early 
Permian faunas of both North America and Europe. The similarities 
between the two continents are so great that it seems highly probable, 
as Romer argued, that there was direct and intimate connection 
between the two areas. Whether or not this type of fauna spread 
beyond the limits of the two continents is not known. 

2. Early Permian (Autunian): The most complete vertebrate- 
bearing early Permian section in North America is found in the red 
beds of north central Texas. An excellent fauna has also come 
from the Abo (Cutler) of New Mexico, and a small, but most in- 
teresting series of assemblages is known from the Dunkard Formation 
of Ohio, West Virginia, and Pennsylvania. The Texas section may 
be extended into Oklahoma, where sporadic finds indicate a verte- 
brate fauna similar, in many respects, to that of Texas, but different 
in some important details. 

The Texas section and probable time equivalents of the Abo 
and Dunkard are shown below: 

Texas New Mexico Ohio, West Virginia, 

Pennsylvania 

( Choza 

Clear Fork Group J Va le 

' Arroyo 
Clyde 

Belle Plains 

Wichita Group J Admiral ^ Dunkard 

Putnam 
( Moran ? ? 

The faunas of Wichita age in Texas, New Mexico, Ohio, West 
Virginia, and Pennsylvania, while similar in higher categories, show 
many detailed differences. They indicate a geographic variation 



390 



FIELDIANA: ZOOLOGY, VOLUME 37 
Table 1. DISTRIBUTION OF REPTILES 









North America 


Western Europe 


Russia 


Africa 


Late 

Permian 

(Thuringian) 






Therapsids 


Therapsids 


Therapsids 






Diadectomorphs 


Diadectomorphs 


Diadectomorphs 








Pareiasaurids 


Pareiasaurids 


Procolophonids 
Pareiasaurids 




L 








Therapsids 
Titanosuchids 


Therapsids 










Titanosuchids 




M 






Tapinocephalids 
Anomodonts 


Tapinocephalids 






Pelycosaurs 
Sphenacodonts 
Edaphosaurians 
Caseids 

Captorhinomorphs 

'Therapsids 
Anomodont-like 


Anomodonts 


Middle 






Pelycosaurs 


Theriodonts 


Permian 
(Sazonian, 






Ophiacodonts 
Diadectomorphs 


Gorgonopsians 
Therocephalians 


Kazanian) 


E 




Procolophonids 
Pareiasaurids 


Pelycosaurs 

Sphenacodonts 
Diadectomorphs 












Pareiasaurids 












?Captorhinomorphs 






C 


Pelycosaurs 










C 

1 


h 
o 

z 


Sphenacodonts 
Edaphosaurians 
Caseids 










e 
a 


a 


Captorhinomorphs 










Pelycosaurs 






r 


V 


Sphenacodonts 
Edaphosaurians 










F 


a 
1 


Caseids 
Captorhinomorphs 










o 


e 


Diadectomorphs 










r 




(basal only) 










k 




Diadectids 








Early 














Permian 






Pelycosaurs 








(Autunian) 


G 

r 
o 
u 
P 


A 

r 
r 
o 
> 
o 


Ophiacodon's 
Sphenacodonts 
Edaphosaurians 
Edaphosaurids 
Captorhinomorphs 
Diadectomorphs 












Diadectids 












Pelycosaurs 


Pelycosaurs 








W 


Ophiacodonts 


Sphenacodonts 








i G 


Sphenacodonts 


Edaphosaurians 








c r 


Edaphosaurians 


Edaphosaurids 








h o 


Edaphosaurids! Diadectomorphs 








i u 


?Caseids Diadectids 








t p 


Captorhinomorphs 








a 


Diadectomorpha 










Diadectids 












Pelycosaurs 


Pelycosaurs 










Ophiacodonts 


Ophiacodonts 






Pennsylvanian 




Edaphosaurians 


Sphenacodonts 






(Stephanian) 




Edaphosaurids 
Captorhinomorphs 


Edaphosaurians 

Edaphosaurids 

Captorhinomorphs 







OLSON: EVOLUTION OF PERMIAN REPTILIAN FAUNA 391 

in North America, during the early Permian, as great as that be- 
tween North America and Europe at the beginning of the period. 

The only known continuous sequence of early Permian verte- 
brates is from Texas, and it is from this area that most of our 
knowledge of faunal evolution in the early Permian has come. There 
is a recognizable, reasonably coherent fauna throughout the early 
Permian, but there are important changes in composition and these 
have an important bearing on the constitution of the mid-Permian 
assemblage. The most important among the changes are as follows: 

Captorhinomorpha: Very primitive, carnivorous to omnivorous 
genera occur in the lowest part of the section (Proterothyris, Romeria) . 
These are replaced by the well-known genus Captorhinus in the 
middle Wichita. A larger genus, Labidosaurus, is present with 
Captorhinus during the Arroyo. With the inception of the Vale, 
the captorhinomorphs began a rather extensive adaptive radiation 
that produced herbivores found in the Vale and Choza. There are 
four genera known from the Vale: Captorhinus, Captorhinikos, 
Captorhinoides, and Labidosaurikos. All except Captorhinoides occur 
in the Choza. It is significant that after the very early Wichita 
all captorhinomorphs were either omnivores or herbivores and that 
the early carnivorous potential was not realized within the order. 

No captorhinomorphs are known in post-Stephanian times in 
Europe. The record during the Autunian is poor, yet it seems 
probable that had the captorhinomorphs undergone a development 
comparable to that in the New World some record would have come 
to light. This absence, if real, may have had an important bearing 
on the evolution that produced the mid-Permian fauna of Europe. 

Diadectomorpha: In the Texas beds there is but a single genus 
of this group, Diadectes. Diasparactus, Diadectes, and possibly a 
third genus are known from New Mexico, and Desmatodon is present 
in the Dunkard. So far as is now known, Diadectes did not persist 
beyond the lowest Vale time. At least two genera of diadectids are 
present in the Autunian of western Europe. Presumably this family 
formed an important element of the fauna. 

Pelycosauria: Ophiacodonts are prominent during the Wichita 
and persist in very reduced numbers into the early Clear Fork. 
Thereafter they are unknown. These primitive pelycosaurs probably 
came from the early captorhinomorphs and have emphasized the 
carnivorous potentials of that group. Sphenacodonts persist into 
the mid-Choza, into the youngest vertebrate-producing beds of the 
Clear Fork. There is considerable diversity of genera and species 



392 FIELDIANA: ZOOLOGY, VOLUME 37 

in the Wichita and the Arroyo, but thereafter only a single species, 
Dimetrodon gigashomogenes, is present. 

The two families of the edaphosaurians have very different 
histories and must be considered separately. There is diversity of 
the Edaphosauridae in Wichita times. One genus, Edaphosaurus, 
persists through the Arroyo. A single specimen of the family 
Caseidae is known from the Abo of New Mexico, but the family is 
not known from the Texas section until the beginning of the Vale. 
Three temporally successive species of Casea occur in the Vale and 
Choza. A second genus, Cotylorhynchus, is present in the Hennessey 
Formation of Oklahoma, a Vale or Choza equivalent. 

Sphenacodonts and edaphosaurids are known from the western 
European Autunian. As in North America, the genus Edaphosaurus 
is present, but in Europe this genus alone represents the family. 
Three genera of sphenacodonts are recognized by Romer and Price 
(1940). Haptodus, which is at about the same level of development 
as Sphenacodon and Dimetrodon, is much the best known. Caseids 
have not been found in the Old World. 

The fauna of the European Autunian resembles that of the very 
early Permian of North America in the presence of Edaphosaurus 
and sphenacodonts. The case for continuity of the continents, 
however, is not particularly strong, for the two faunas could have 
been derived independently from the common Stephanian fauna. 
Also, the degree of divergence of the mid-Permian faunas of the 
Old and New Worlds indicates that separation had occurred well 
down in the early Permian. 

No other Autunian faunas have been described, although Price, 
in informal communication, has indicated that there may be an 
Arroyo equivalent in Brazil. The latest early Permian assemblage 
in North America includes sphenacodonts, caseids, and captorhino- 
morphs. Of these, only the first is known from the early Permian 
of Europe. 

3. Mid-Permian. The mid-Permian faunas of Russia and 
South Africa differ markedly in constitution from the earlier Permian 
assemblages of either North America or western Europe. Therapsids 
and diadectomorphs are the principal reptiles. The diadectomorphs 
are pareiasaurs and procolophons, rather than diadectids. There 
are only remnants of pelycosaurs. No captorhinomorphs are known 
from Russia. One family, Milleretidae, has been reported from 
South Africa, but, as Broom (1938), who described the material, 
has noted, the assignment is open to doubt. 



OLSON: EVOLUTION OF PERMIAN REPTILIAN FAUNA 393 

The North American assemblage. The families of reptiles in the 
North American mid-Permian are the same as those in the late 
Clear Fork, except for the family of one genus, Dimacrodon, which 
has therapsid affinities. The change, at the generic level, is striking. 
It seems improbable that the mid-Permian fauna was derived directly 
from the known fauna of the Choza. Of the reptiles, only Coty- 
lorhynchus, which is present in the Hennessey of Oklahoma, has been 
found in earlier beds. Most striking is the strong tendency toward 
large size. There existed forms that approximate pareiasaurs, 
titanosuchids and tapinocephalids in general dimensions and bulk. 
There appear to be strong resemblances in the types of changes 
and adaptations in the New and Old Worlds, but changes that 
stemmed from very different immediate ancestors. The reptiles of 
Russia and South Africa have been thoroughly described in such 
general works as Romer (1945), Broom (1932), von Huene (1940), 
and Olson (1944). The North American materials have been but 
recently discovered and have only been described briefly (Olson 
and Beerbower, 1953). The salient features of this fauna are as 
follows : 

Seven genera of reptiles have been identified from the San 
Angelo and Flower Pot Formations of Texas. In addition, xenacanth 
sharks and a problematic amphibian jaw have been found. The 
ranges and numbers of specimens are shown in Table 2. It has 
been noted that the mid-Permian reptiles were strikingly larger 
than the largest of their immediate predecessors. Table 3 gives 
examples of the differences, based on comparisons of available 
materials. 

The identified genera and their principal characters are as follows : 

Rothia: This is a large captorhinomorph which probably ran 
from five to six feet in length. The skull was heavy and the palate 
was set with long, irregularly spaced teeth. The animal was un- 
doubtedly a herbivore and probably was somewhat like the edapho- 
saurids in habits. There is no certain ancestor among known 
captorhinomorphs. 

Steppesaurus: This is a large sphenacodont, about one-fifth to 
one-fourth larger than the largest known specimens of Dimetrodon. 
Like Dimetrodon, it had greatly elongated neural spines. The spines 
and general structure suggest that it arose from Dimetrodon. Dime- 
trodon was widespread through Oklahoma and Texas during the 
Clear Fork and appears to have crossed boundaries between adjacent 
ecosystems. 



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OLSON: EVOLUTION OF PERMIAN REPTILIAN FAUNA 395 

Tappenosaurus: This carnivorous reptile was the giant of the 
fauna. It probably stood about 5 feet at the shoulder and, assuming 
a sphenacodont type of tail, was at least 18 feet in length. What 
is known of the skull indicates sphenacodont affinities, but there is 
no known ancestor in the earlier Permian. 

Cotylorhynchus: This genus occurs in the Hennessey Formation 
of Oklahoma. The San Angelo-Flower Pot representative is about 
one-fourth larger than the Hennessey species. Cotylorhynchus was 
a herbivore of caseid affinities. 

Caseoides: This genus is somewhat larger than Casea halselli 
from the Choza but could well have been derived from the genus 
Casea. It is one of the commonest genera in the San Angelo-Choza 
and probably was an important element of the fauna. Its adaptive 
characters appear to be similar to those of the late Vale and Choza 
species of Casea, for it was evidently a slow-moving, herbivorous 
inhabitant of flood plains and margins of bodies of standing water. 

Angelosaurus: This genus has been tentatively assigned to the 
Caseidae. It was a large, clumsy herbivore with short limbs and 
relatively enormous feet. The body structure tended to be massive 
throughout. There is no known ancestor of Angelosaurus in the 
earlier Permian. 

Dimacrodon: This genus has been tentatively assigned to the 
Therapsida. Unfortunately it is known largely from jaws and skull 
fragments. It has a pair of enlarged "canine" teeth and small 
post-canine teeth. There were no "incisors" and the broad sym- 
physis of the lower jaw probably was covered by a horny beak. 
There are no certain ancestors in the earlier Permian. It is quite 
possible that this "therapsid" was from a sphenacodont stock and 
that it evolved independently of the Old World therapsids. 

There are uncertainties in the correlations between the three 
areas that are our chief concern and at present there is no way of 
resolving the difficulties. Presumably the greatest hope lies in the 
use of botanical remains, but the materials necessary have not as 
yet been obtained. The North American deposits have been placed 
in the mid-Permian on the basis of local stratigraphic and faunal 
evidence (see Olson and Beerbower, 1953). The same in general is 
true for the Russian and South African deposits. The North 
American deposits are certainly no younger than earliest mid- 
Permian, but they lie above typical terrestrial Leonard deposits. 
This assignment compares favorably with that made for Zone I 
(Rhopalodon Zone) and, perhaps, Zone II (Titanophoneus Zone) of 



396 



FIELDIANA: ZOOLOGY, VOLUME 37 



Table 3 MEASUREMENTS OF GENERA OF SAN ANGELO 

REPTILES AND COMPARATIVE MEASUREMENTS OF 

VARIOUS GENERA FROM EARLIER PERMIAN 

Based on largest known specimens from both San Angelo 
and earlier Permian ; measurements in centimeters. 







Rothia 








Genus 


Probable total 
length 


Skull 
length 






Rothia 

Labidosaurus . 
Labidosaurikos 
Captorhinus. . 
Captorhinikos . 


165 

90 

165 

35 

50 

Steppesaurus 


26 
20 
30 

8 
10 






Genus 


Jaw length 


Ulna length 




Steppesaurus . 
Dimetrodon . . . 


59 

39 


27 
20 




Genus 


Est. total 
length 


Tappenosaurus 

Femur Humerus Pelvis 
length length height 


Centrum 

length 
dors. vert. 


Tappenosaurus . 
Dimetrodon 


540 

328 


50 45 

27 24 


55 


7.6 
5.2 




Genus 


Dimacrodon 


Jaw length 






Dimacrodon 

(no comparative material) 


20 (est.) 






Cotylorhynchus 
Genus and species 


Humerus 
length 






Cotylorhynchus 
Cotylorhynchus 


hancocki (San Angelo) . . 39 . 
romeri (Hennessey) .... 31.5 








Caseoides 






Genus and species 


Humerus 
length 


Femur 
length 


Prox. width 
femur 


Caseoides 

Casea broilii (Lower Vale) 

Casea nicholsi (Upper Vale) .... 
Casea halselli (Middle Choza) . . 


15.7 

. 7.2 
10.0 


14.5 
8.5 

8.5 


7.3 
2.5 
3.9 
6.3 


Humerus 
Genus and species length 


Angelosaurus 

Centrum 
Femur length 
length dors. vert. 


Pubo-isch. 

symphysis 

length 


Angelosaurus. . . 
Casea nicholsi . . 
Casea halselli . . . 


18.9 
10.0 


21.6 
8.5 


3.9 
2.3 
2.9 


19.5 
12.2 
19.2 



OLSON: EVOLUTION OF PERMIAN REPTILIAN FAUNA 397 

Russia. The earliest Russian beds in which vertebrates are found 
are generally considered slightly older than the earliest producing 
beds of the African Beaufort Series (Tapinocephalus Zone). This 
relationship is based largely on local stratigraphic evidence and upon 
the contained faunas. More important than the precise time rela- 
tionships between the areas, however, is the fact that more or less 
equivalent evolutionary levels have been reached in Russia and 
South Africa and that a somewhat similar adaptive stage is recorded 
in the San Angelo and Flower Pot Formations of North America. 
There is an event equivalence, even though some time differences 
may exist. 

EVOLUTIONARY RESEMBLANCES AND DIFFERENCES BETWEEN THE 
MID-PERMIAN OF THE OLD AND NEW WORLDS 

If the taxonomic differences between the mid-Permian reptiles 
of the Old and New Worlds are ignored, and adaptive types con- 
sidered, striking resemblances become apparent. Most obvious is 
the comparable large size of a number of the animals in both areas. 
This relative gigantism is spectacular in North America, coming as 
it does shortly after the disappearance of the typical, deltaic fauna 
of the early Permian, where proportions are more modest. The 
giants of the earlier Permian were Dimetrodon and Cotylorhynchus. 
The marked increase of the mid-Permian Steppesaurus and Coty- 
lorhynchus over their predecessors has been noted. More amazing 
is the great size of Tappenosaurus. Equal size is recorded in titano- 
suchids, tapinocephalids, some theriodonts, and the pareiasaurs in 
the mid-Permian of Russia and South Africa. Here the size seems 
less striking, in the lack of knowledge of earlier faunas. 

Resemblances go far beyond the mere coincidence of size, and 
extend to more specific adaptations. The adaptive resemblance of 
Tappenosaurus to the titanosuchids is clear. It can hardly be denied 
that they represent parallel trends from a common, but somewhat 
remote sphenacodont ancestry. The analogy between Steppesaurus 
and such theriodonts as the gorgonopsians and early therocephalians 
is evident. Steppesaurus is an adaptive relict in the mid-Permian, 
for it changed little, in an adaptive sense, from Dimetrodon of 
earlier times, although it was involved in a very different ecological 
situation. The stability of Dimetrodon itself under changing con- 
ditions is well shown by the persistence of the genus for nearly the 
full span of the early Permian, and the persistence of a single species, 
D. gigashomogenes, through most of the Clear Fork. A similar genus, 



398 FIELDIANA: ZOOLOGY, VOLUME 37 

Steppesaurus, appears to carry on this tolerance, as it occupies a 
theriodont-like place in the mid-Permian fauna. The two known 
carnivores of the San Angelo and Flower Pot find close parallels in 
the principal carnivores of the mid-Permian of Russia and South 
Africa, the titanosuchids and the theriodonts. 

The situation with respect to herbivores is more difficult to 
visualize, for there is less actual resemblance in form, and evidence 
of the ecological positions in the economy of the fauna must be the 
principal basis for judgment. The closest morphological resem- 
blance, so far as known structures are concerned, is between Dimac- 
rodon and some of the early anomodonts. In the broad symphysis 
of the jaws, the presumed horny beak, the large "canines" and 
small post-canines, they are very similar. It seems highly im- 
probable, from the differences in the rest of the faunal elements 
and geographic remoteness, that there was anything but a rather 
remote common ancestry, so that this would appear to be a valid 
case of parallelism, or, perhaps, convergence. 

The remaining herbivores are captorhinomorphs or caseids in 
North America, in contrast to the anomodonts, tapinocephalids, 
pareiasaurs, and procolophonids in the Old World. Angelosaurus 
and Cotylorhynchus were large, slow-moving vegetarians that must 
have provided an important food supply for the large carnivores. 
In this sense they were associated with the vegetation on the one 
hand and the predators on the other in much the same way as were 
the tapinocephalids and pareiasaurs. Neither of the North American 
genera had a skeletal structure as massive as that of these two types, 
nor had they assumed as upright a pose. Nevertheless, they repre- 
sent marked departures from the earlier herbivores of Texas and 
their differences appear to be directly related to their place in the 
changed ecological situation. The development of the pareiasaurs 
and tapinocephalids similarly can be presumed to have taken place 
during the evolution that led to the large Old World carnivores. 

Rothia and Caseoides, both of which are more frequently en- 
countered in the deposits than the larger herbivores, fill the position 
of the smaller plant-eaters, occupied in large part by the anomodonts 
in the South African and Russian mid-Permian. 

Here the analogy ends, for we are faced with the puzzling fact 
that at present almost no traces of animals smaller than Rothia 
have been found in the San Angelo or the Flower Pot. This is true 
in spite of the fact that types of deposits, which, in earlier sequences, 
have yielded an abundance of small vertebrates, have been explored 



OLSON: EVOLUTION OF PERMIAN REPTILIAN FAUNA 399 

thoroughly. During the last year, beds in swamps and swamp 
margins that were rich in large vertebrates and in plants have been 
combed, without the discovery of small reptiles, amphibians, or fish. 
These studies have led to the interpretation of the San Angelo and 
Flower Pot faunas as marginal phases of better-integrated faunal 
units that included all elements necessary to a balanced economy 
(Olson and Beerbower, 1953). There are no counterparts of pro- 
colophonids, small anomodonts, or small theriodonts in the San 
Angelo-Flower Pot fauna. 

ORIGIN AND EVOLUTION OF THE NEW AND OLD WORLD 
MID-PERMIAN FAUNAS 

A coherent interpretation of the origin and evolution of the 
faunas requires certain assumptions. It is assumed that the faunas 
in the Old and New Worlds arose from a common ancestral Penn- 
sylvanian stock. This stock is considered to have been spread, 
with continuity, over both the Old and New Worlds. Such evidence 
as we have concerning the Pennsylvanian supports this hypothesis. 
It is assumed, further, that the common characteristics of the fau- 
nas of the Old and New Worlds appeared at more or less the same 
time, during the late part of the early Permian. We know that the 
elements had not appeared in North America prior to this time and 
such evidence as there is of the early Autunian of Europe gives no 
suggestion of their presence in Europe. A coincidence of conditions 
favoring increased size and other adaptive similarities and evolu- 
tionary thresholds that permitted exploitation of these conditions 
must have occurred in both areas. In other words, in both the Old 
and New Worlds there existed in the late part of the early Permian 
comparable opportunities and stocks able to take advantage of 
these opportunities. While the opportunities may well have been 
much the same, the stocks seem to have been very different. 

What is known of the early Permian faunas in western Europe 
gives some indication that differences may have been initiated by 
that time. So far as we know there were no caseids and no capto- 
rhinomorphs present. These, however, are dominant elements of 
the late early Permian in North America, and captorhinomorphs 
were abundant during all of early Permian. Sphenacodonts, 
edaphosaurids, and diadectids were present in the early Permian of 
the Old World. In North America diadectids and edaphosaurids 
gave way to the caseids and captorhinomorphs during the late part 
of the early Permian. In the Old World the edaphosaurids failed, 



400 FIELDIANA: ZOOLOGY, VOLUME 37 

but the procolophonids and pareiasaurs, presumably diadectid 
descendants, give indication that this group was successful. 

The predominant reptilian types of the early Permian in western 
Europe were the sphenacodonts. It is from this stock that the 
therapsids appear to have stemmed. If this is the case, there must 
have been a rapid and pronounced adaptive radiation of this group 
late in the early Permian, to produce both herbivores and carnivores. 
In the absence of captorhinomorphs and caseids, which maintained 
a balance with carnivorous sphenacodonts in North America, such 
a radiation would be a most probable event. The only reptilian 
competition to the herbivore radiation would have been supplied 
by the relatively unprogressive diadectomorphs. The radiation 
would compare in part to the rapid adaptive changes in the capto- 
rhinomorph stock in North America, a radiation that appears to 
have filled the gap left by the disappearance of the diadectids and 
edaphosaurids. It would compare as well, once herbivores had 
been established, with the caseid radiation that began in North 
America during the Vale. 

The difference in stocks of the herbivores may be supposed to 
have had an important impact on the carnivores. In the Old World, 
under the hypothesis advanced above, they stemmed from the 
advanced and highly active sphenacodonts, whereas in North 
America, except for Dimacrodon, herbivores developed from the 
relatively unprogressive captorhinomorphs and caseids. Selective 
pressure for activity in the Old World must have been far in excess 
of that in the New. The keynote to the origin and evolution of the 
therapsids and finally to evolution of the mammals, appears to have 
been continued emphasis on activity. Of course there were many 
bypaths, in which ponderous and slow therapsids developed, but 
fundamentally the level of activity in a therapsid-dominated fauna 
must have been higher than that in one where pelycosaurs played 
the primary role. 

We do not as yet know, and may never know, the history of 
reptiles after the early mid-Permian in North America. There is 
little indication in what is known of the early mid-Permian fauna 
that it was likely to approach and pass the therapsid threshold 
necessary to the radiation seen in the Old World. As long as the 
isolation, which must have existed to preserve the pelycosaur- 
captorhinomorph lines in North America, persisted, adaptive modi- 
fications of this stock without "progressive" modifications of funda- 
mental structures would appear to be the most probable course 
of events. 



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Huene, F. VON 

1940. Die Saurien der Karroo-, Gonduana- und verwandten Ablagerungen in 
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Olson, E. C. 

1944. Origin of mammals based upon cranial morphology of therapsid sub- 
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Olson, E. C. and Beerbower, J. R. 

1953. The San Angelo Formation, Permian of Texas, and its vertebrates. 
Jour. Geol., 61: 389-423. 

Romer, A. S. 

1945. Vertebrate paleontology (2nd ed.). Univ. Chicago Press, Chicago. 
661 pp. 

1945. The Late Carboniferous vertebrate fauna of Kounova (Bohemia) 
compared with that of the Texas redbeds. Amer. Jour. Sci., 243: 417-442. 

Romer, A. S. and Price, L. I. 

1940. Review of the Pelycosauria. Geol. Soc. Amer., Spec. Papers, no. 28, 
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